Automatic telephone system



y 1929! w. o. PASSMORE 1,722,538

AUTOMATIC TELEPHONE SYSTEM Filed Oct. 12. 1927 RTE-51F? William P ZE E Passmnr'e Patented July 30,1929.

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WELLIAM OGLESBY PASSIVIORE, OF LIVERPOOL, ENGLAND, ASSIGNOR T0 ASSOCIATED TELEIPI-IONE AND TELEGRAPH 'CGMPANY, OF KANSAS CITY, MISSOURI, GORIORA- TION OF DELAWARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed October12, 1927, Serial No. 225,614, and in Great Britain October 29, 1926.

The present invention relates to automatic or semi-automatic telephone systems and is more particularly concerned with systems in which arrangements are provided such that certain privileged parties such as test clerks or toll operators can connect with busy lines and break down established or partly established connections thereon. loll operators, for instance, will require to down local connections in favor of long distance connections, since these are generally of more importance. The object of the invention is to enable this to be done readily and reliably in all the varied circumstances which are likely to arise in practice.

According to the invention, this is attained in enabling a party, having obtained access to a busy line, to break down an established or partly established connection in response to the connection of a special potential to the speaking leads.

According to another feature of the invention, use is made of a switch adapted to feed current to both calling and called parties in which the feeding bridges comprise in each case a relay connected between one speaking lead and earth and an impedance coil connected between the other speaking lead and battery. With a switch of this type, when a toll operator wishes to break down an existing connection, she applies earth to both speaking leads which is effective to shunt out subscribe either the line relay or the back brid e relay according as the wanted is the calling or called party. equally effective whether or not the calling party has replied and thus effected a reversal of current flow over the calling line.

In orderthat the invention may be more fully understood and readily carried into effect, a telephone system according to the present invention will now be described by way of example with reference to the accompanying drawings. Figure 1 shows a rotary connector switch modified according to the present invention to enable a toll operator to establish connection with a busy party and break down either an incoming or outgoing call.

Although the invention has been shown in Fig. 1 applied to a rotary connector it will be understood that it is equally applicable to regular connector switches, or indeed any be able to break Moreover, it is switches adapted to feed battery to bot-h calling and called parties.

A detailed description will be given of the arrangement shown in Figure 1. lVhen the rotary connector RC is taken into use, impulse receiving relay A energizes in the following circuit: battery, resistance 54, resting contact and armature 32, resting contact and armature d5, normally closed contacts controlled by armature 11, negative line conductor, calling partys loop, positive line conductor, normally closed contacts controlled by armature 12, winding of relay A to earth. Relay A, upon energizing, completes the following circuit for release relay B: earth, armature 16 and its working contact, resting contact and armature 30, winding of relay B to battery, Relay B upon energizing earths the release trunk conductor RT- from earth at the normally closed contacts controlled by armature 10, working contact and armature 18 to release trunk conductor RT; prepares a switch holding circuit at armature 17 and at armature 19 completes the followingcircuit for relay J earth, armature 19 and its working contact, resting contact and armature 29, winding of relay J to battery. Relay J energizes and completes the following looking circuit for itself: battery, relay J, armature l3 and its resting contact, working contact and armature 34, working contact and armature 19 to earth; and at armature 33 prepares the booster battery metering circuit. At armature 20, relay B opens a point in the circuit of release magnet Z and prepares the impulsing circuit.

Relay A now responds to the next series of impulses in the wanted number and effects the operation of the vertical magnet in accordance therewith. The first impulse of the first series is transmitted to the vertical magnot over the following circuit: earth, armature 16 and its resting contact, armature 20 and its workingcontact, normally closed offnormal springs N, vertical magnet V and series relay C to battery. Vertical magnet V and relay 0 energizes in series in this circuit and upon the first vertical step of the switch, off-normal springs N and N operate, so that subsequent impulses are repeated to the ver-- tical magnet as follows: earth, armature 16 and its resting contact, armature 20 and its working contact, spring N and its working contact, armature 26 and its working contact, vertical magnet V and relay C to battery. Relay C which is operated by the first impulse of the series, remains operated owing to its slow-to-release characteristics until all the impulses of the series are completed, after which it restores and switches the impulsing circuit from the vertical magnet V to the rotary magnet R.

The succeeding and final series of impulses is repeated to the rotary magnet R by relay A as follows: earth, armature l6 and its resting contact, armature and its working contact, off normal spring N and its working con tact, armature 26 and its resting contact, resting contact and armature 37, winding of slow relay E, arn'iature 49 and its resting contact, rotary magnet R to battery. In response thereto, rotary magnet E steps the switch shaft and wipers round to the desired contacts in the selected level. Relay E energizes with the first impulse and remains operated throughout the series due to its slow-to-release characteristic. Relay E, upon operating, disconnects the P wiper at armature 39; at armature 40, connects the P wiper over arn'iature 4:8 and its resting contact to relay G; and armature 41, provides an alternative circuit for the remaining impulses as re lay G will energize in case the wipers pass over busy contacts. At the end of the series of impulses, the wipers will be engaging the first line in the required P. B. X. group.

If this line is engaged, wiper P will find earth and the following circuit will be completed for relay G before relay E restores; earth, wiper P armature 40, and its work ing contact, arn'iature 48 and its resting contact, winding of relay G to battery. Relay G then operates and prepares the following locking circuit: battery, relay G, resting contact and armature L8, normally closed contacts controlled by armature 40, working contact and armature 36, normally closed contacts controlled by armature 2st, working contact and armature 17 to earth. Relay G upon I operatmg completes the following circuit for effecting the automatic rotary movement: earth, wiper P (P and P contacts are strapped together on all but the last line of the group) resting contact and armature 39, armature and its working contact, rotary interrupter springs 51, winding of relay K which is at this time shunted by resistance 54 and armature 25,, winding of relay C to battery. Relay C operates in this circuit and at armature 25 removes the shunt from relay K and permits relay K to. operate. Relay K upon operating completes the following cir cuit for the rotary magnet R earth, armature 17 and its working contact, armature 22 and its working contact, armature 49 and its resting contact, winding of rotary magnet R to battery. Rotary magnet R operates and advances the wipers on to the next set of contacts. When the armature of the rotary magnet is fully attracted, the interrupter springs 51 open the circuit of relays K and G, and relay K restores and opens the circuit of the rotary magnet at armature 22. Relay 0, how- P ever, does not release this time due to its slow-to-i'elease' characteristic and during the time that relay C remains operated the earth on wiper P maintains relay G energized. Relay G is slightly slow to release and should the private wiper P while rotating fail to bridge two adjacent busy contacts thereby disconnecting earth, relay G will remain operated until wiper P finds earth at the next contact. If the next line is engaged, private wiper P will continue to find earth and relay K will operate again and operate rotary magnet which will again step the wipers and so on until the last line of the group is reached unless a free line is encountered previously. When the last line of the group is reached, wiper P will not find earth on the private bank as the private bank contacts of this line are not strapped together, and therefore relays K and C will restore. Relay K, in releasing, extends the busy circuit from conductor BS over armature 23 and armatures 42 and 88 to the positive line conductor. The calling party on hearing the busy signal will replace his receiver, causing relays A and B to deenergize and complete the following circuit for release magnet Z: earth, armature 16 and its resting contact, armature 20 and its resting contact, elf normal springs N and release magnet Z to battery.

In case all the lines are not engaged, the private wiper P instead of finding earth on the private bank contact of a free line will find battery from the called subscribers cutoff relay, and when relay G restores the following circuit is therefore completed for switching relay H; earth, armature 17 and its working contact, normally closed contacts controlled by arniature 24, armature and its resting contact, lower winding of relay H, resting contact and armature 40, wiper P to battery via the called subscribers cut-off relay. Relay H, upon operating, at armature 4'? locks up over its upper winding to earth at armature 17 of relay B. The cut-off relay of the line-switch operates in series with the lower winding of relay H and is maintainedv operated by earth at armature 17 which extends over armature 46 and its working Contact to wiper P At armature 4C5, battery through resistance 54 is disconnected from the line conductor L, and battery through the lower winding of impedance I is connected thereto instead. l he operation of relay H also opens the rotary magnetcircuit at armature 49 to prevent further rotation, should the calling subscriber inadvertently operate his calling device; and at armatures 43 and 50 completes the ringing circuit, Interrupted ringing current is now supplied from the generator lead GEN, upper winding of ringing trip relay F, resting contact and armature 27, working contact and armature 43 to the negative speaking conductor through the called partys bell and condenser to the positive speaking conductor, armature 50 and its working contact, armature 32 and its resting contact, resistance 54 to battery. An indication that the called subscribers bell is being rung is given to the calling subscriber by an audible signal in his receiver since a small amountof ringing current flows over armature le: and small condenser 52. On the called partys removing his receiver, relay F operates and closes a locking circuit for itself at armature 2S and cuts oii" the ringing current at the resting contacts of armatures 27 and 32 and at these same armatures completes the talking circuit. Current for speaking purposes is supplied to the called party from the upper winding of the impedance coil I and through the reversing relay D. As soon as this connection is established, relay D operates and reverses the direction of the currentflow over the incoming speaking conductors, battery being connected to the incoming positive conductor from the lower winding of impedance coil 1, armature 12 and its working contact, and earth to the incoming negative conduct-or through the winding of relay A and armature 11 and its working contact. Vhen relay D operates, it also breaks the circuit of relay J at armature 13, but relay J being slow to release does not fall away immediately. Nhile it holds up, booster battery from conduct-or BM is connected over, resistance 53, armature 33 and its working contact, armature 10 and its working contact, working contact and armature 18 to the release trunk conductor RT and thereby operates the calling partys meter. After an instant relay J releases and disconnects booster battery from the release trunk, replacing the booster battery by earth potential at the normally closed contacts controlled by armature 33. The connector shown in Figure 1 is suitable also for dealing with individual lines in which case the bank contacts accessible to wipers P and P are not strapped together and therefore no automatic rotary operation will take place.

In order to explain the feature of the in vention whereby an operator can release an established connection for the purpose of set ting up a trunk call, it will be assumed that the connector has just established connection with a wanted party and that a trunk call then arrives for this party. The toll operator then extends a connection to the wanted line over atoll switching train by dialling his number in the usual manner and then connects earth to both speaking concuctors, by the operator depressing a special key. The

nect of earth in the positive conductor is to short-circuit relay D while that on the negative line does not perform any useful function at this instance. Relay D releases and at armature 14 opens the circuit of re lease relay B. Relay B, upon deenergizing, removes earth at armature 18 from the relcasetrunk, thereby allowing the preceding switches to release.

l Vhen the preceding switches have released, relay A deenergizes owing to the opening of its circuit and completes the following circuit for the release magnet Z; earth, armature 16 and its resting contact, armature 20 and its resting contact, off-normal springs N winding of magnet Z, battery. It may be mentioned at this point that the switch which establishes connection with an engaged line can be arranged to give the calling party a distinctive warning signal to indicate that the connection is wanted for a toll call and will be shortly disconnected.

Consider now the case in which the operator has a toll call awaiting subscriber who is already engaged in an outgoing call set up over the connector shown in 1. Under these conditions the operator extends a connection to the wanted line over a toll switching train by dialling the Wanted number and then connects earth to both positive and negative speaking conductors as before. In this case the calling partys loop is holding relay A of the connector.

Assume first, that the called party has not yet answered and that accordingly relay D has not yet operated. The connection of earth potential to the incoming positive line will in this case short-circuit relay A causing it to deenergize and open the circuit of relay B. With relays A and B in deenergized condition, the circuit of the release magnet is closed, and holding potential is removed from the release trunk conductor so that the whole connection is cleared down.

Assume now that the wanted party has answered thecall when the operator establishes connection with the calling partys line. Under these conditions relay D will be in 0perated position and the earth on the incoming negative conductor will now bring about the release of relay A with the results previously described. It will thus be seen that by connecting earth potential to both con ductors it is possible to bring about the release of the switch in either of the above two conditions.

What is claimed is:

1. In. an automatic switch having a trunk terminating therein, a single wound line relay for controlling the operation and release of said switch normally connected to one conductor of said trunk line, and means for connecting said relay to the other conductor of said trunk line under certain conditions, said relay being maintained energized over its one winding only so that it will release when a certain potential is applied to both con- 'ductors of said trunk line to cause the release of said switch regardless of which conductor said relay is connected to.

2. In a telephone system, an automatic switch, a trunk line terminating in said switch, a line relay normally connected to one conductor of said trunk line for controlling the operation of said switch to extend a connection to a called party, means for connecting said relay to another conductor of said trunk line operative when the called p arty answers, and means for causing said line relay to release said switch responsive to the application of a certain potential to both said conductors regardless of whether the called party has or has not answered.

3. In a telephone system, a connector switch for extending a call to a called line and for signalling the called subscriber, a ring-cutofl relay for interrupting the signalling when the call is answered, a back-bridge relay energized responsive to the operation of said ringcut-olf relay, and a release relay initially energized over a circuit including normally closed contacts on said ring-cut-oli' relay and subsequently energized over a circuit including contacts closed by the operation of said back-bridge relay so that the release of said switch is under the control of said back bridge relay after the call isanswered.

4:. In a telephone system, a connector switch for extending a call from a calling to a called line, a line relay in the switch controlled over the calling line, a back-bridge relay in the switch controlled over the called line, a release relay for controlling the release of the connector energized over a circuit including contacts on said line relay, and means responsive to the answering of the call for including contacts on said back-bridge relay in said circuit.

5. In a connector switch for extending a connection, a line relay, a back-bridge relay,

a release relay responsive to the operation of said line relay, and means effective after said back-bridge relay has been operated to cause the restoration of said release relay responsive to the release of said back-bridge relay.

In witness whereof, I hereunto subscribe my7name this 15th day of September, A. D. 192

WILLIAM OGLES BY PASSMORE. 

